AD is a common internal tangent to circles B and C. Find the length of the radius of circle B. Round to the nearest hundredth.

As AD is common tangent,
<BAE=90=<CDE
Also <BEA=<CED as they are opposite angles
By AAA, the two triangles, ABE and DCE, are similar
so AB/EA = DC/ED
AB = EA * DC/ED = 18 * 4/6
= 12